One of the most common misunderstandings among both clients, and unfortunately many designers, is the difference between Vector and Raster (also known as Bitmap) graphics. This short summary is a reference to our clients as an attempt to articulate the primary differences between these two graphic types and explore the areas where usage of each is most appropriate.

It is worth mentioning in advance, because it is a critical point, that when we refer to Raster and Vector graphics, we are not referring to any particular file format or extension. Though file formats are typically responsible for saving one type of graphic or another, the distinction between Vector and Raster is independent of any assigned extension.

Raster Graphics are the most common graphic format in use on the web and, indeed, on the computer. Raster graphics are composed of pixels, each of which contains specific color information. A single image may be composed of hundreds of thousands of individual pixels. Much like cells revealed from a piece of tissue when seen under a microscope, these pixels are only clearly and individually visible when the image is magnified (Figure 1).

Making an existing Raster graphic smaller is a process of reduction; pixels are removed from the image until it fits the new size. Computers are well equipped to perform this task. An image can be sized smaller repeatedly and still maintain the same quality, up until the point where there are not enough pixels available to reproduce the image clearly.

To increase the size of a Raster image, the computer must ADD additional information (pixels) to the original image to allow it to fill the new larger area. Since there is no source for this information, it must be interpolated based on what is currently available in the image. Because the computer is not especially skilled at guessing games, Raster images that have been SCALED LARGER are frequently blurry and we cannot use them for sublimation. (Figure 2)

Vector Graphics are mathematical creations. For this reason, the programs that are used to create them save instructions on how the image should be drawn, rather than how it looks. Instead of being composed of pixels, Vector graphics consist of points, lines, and curves which, when combined, can form complex objects (Figure 3). These objects can be filled with solid colors, gradients, and even patterns.

Because the computer has a description of how the image should look, it can be redrawn at any size, in any position, without losing any quality. A vector graphic resized to 5 times its original dimensions is simply reproduced, exactly, at the new size. It can also be freely manipulated without losing coherence, like a rubber band that can be stretched an infinite number of ways.

The price of this scaling flexibility is that Vector images must remain relatively simple in comparison to Raster images. It is impossible to render the nuances of a photographic image in a vector editor; as a result, illustrative vector graphics have a distinct look and feel, even when produced in detail.

However, Vector graphics are ideal for producing artwork which frequently needs to be presented in different sizes or colors. Logos especially fall into this category. A logo produced with a vector application can be blown up to fit on a billboard or scaled down to adorn a letterhead with no loss of quality (Figure 4).

What are some common Raster editors and file formats?
Adobe Photoshop, Corel PhotoPaint, and Macromedia Fireworks and Paint Shop Pro are just a few of the more popular Raster Editors. Common raster file extensions include: .jpg, .gif, .png, .tff, and .bmp.

What are some common Vector editors and file formats?
Adobe Illustrator, Corel DRAW!, Macromedia Freehand, and Macromedia Flash are the predominate editors on the market. Common universal file formats include .eps and .wmf and .svg. Unlike Raster graphics, it is far more likely to see Vector files delivered in formats unique to the programs which created them. Some popular program specific extensions include .ai (Adobe Illustrator), .cdr (Corel Draw), and .fla/.swf (Macromedia Flash). We use Adobe Illustrator.

If a Raster graphic is pasted into a Vector editor, does it automatically become Vector?
Once a Raster graphic, always a Raster graphic. Although most Vector applications are able to display Raster images as embedded objects (and many applications even include a limited set of tools to manipulate them) their inherent format does not change. The only way to convert a Raster image to a Vector image is to trace the image using either a manual process or automatic program.

The tracing process attempts to duplicate the shapes of a Raster image using Vector lines and curves. When Vector graphics are pasted or imported into Raster editors, however, the opposite is true. The editor converts the vector image to Bitmap as soon as it is brought in. Once a Vector image is converted to Raster image, there is no way to return to the original state. For this reason, Designers keep copies of the original vector artwork when converting an image to a raster file format.